1. Field of the Invention
The present invention relates to the field of substrate processing using a plasma. More specifically, the invention relates to an apparatus for protecting the walls of a processing chamber having interior walls subject to erosion, general wear and contamination of the chamber walls from chemical reactions and physical effects of plasma processing.
2. Background of the Art
Plasma processing is used in the manufacture of various types of articles including semiconductor integrated circuit devices. Plasmas may be used to provide ions to sputter a target and thereby free atoms or larger particles of target material for deposition on a surface such as a semiconductor substrate. Plasmas may also be used to provide an environment for etching layers of material formed on a surface such as a semiconductor substrate. The plasma may be created by flowing a quantity of gas through a vacuum chamber maintained at a subatmospheric pressure, e.g., 10.sup.-3 Torr, and then exciting the gas with an electric field to disassociate the gas molecules to provide free gas ions and excited state species. The chamber must of course be constructed of a rigid metal, often aluminum, in order to contain such a quasi vacuum. The chamber is supplied with gases for processing the articles and a source of electric current. Often such a plasma processing chamber accommodates single articles at a time, but the chamber can also be designed for processing a plurality of articles simultaneously.
In some plasma processes, the gases used, as well as the presence of ions in the plasma, can cause erosion and wear of the reaction chamber walls. Also the metal material of the chamber walls, if exposed to corrosive gases or plasma, could react with the gases or plasma and form undesirable byproducts contaminating the processing chamber. One prior art approach to this problem is to anodize the chamber walls in order to provide a substantially inert surface on the metal walls. Moreover, anodization provides a hardness to the metal wall surface that enables the wall surfaces to withstand ion sputtering more effectively than without anodization. Eventually, however, the anodized layer is sputtered or etched off, since even an anodized surface still is subject to some degree of reactivity with the gases or plasma. Once the anodization wears off, the chamber itself must be replaced.
To prolong the lifetime of the chamber walls, shields are used to cover and thereby protect the walls from the gases and the plasma. These shields are formed preferably from material similar to that of the wall, and are anodized on the outer surfaces. The shields are placed inside the chamber as close as possible to the walls so that the wall material is protected from the action of the plasma and gases. However, the shields do not make effective electrical contact with the walls. The rigidity of the shields makes it more likely that corrosive or depositing gases can reach the wall through voids between the shields and wall because the rigidity of the shield prevents the shield from fully conforming to the contours of the wall. The lack of an effective electrical connection to the walls causes the shields to electrically float in the plasma, thereby creating a surface on which electrical charge could build and eventually form an arc in the plasma due to the charge leaking to another part of the chamber. Such plasma arcing is potentially highly damaging to the interior of the processing chamber or to the substrate being processed.
There is a need for a protective shield for the chamber walls that effectively protects the walls from wear and corrosion by minimizing the ability of gases and plasma to come into contact with the walls. It would be additionally very desirable to design a shield to minimize arcing. It would be advantageous if the shield were in addition inexpensive and easy to remove and install.